Internal combustion engines such as diesel engines and gasoline engines use injectors to introduce fuel into combustion chambers of the engine. Two types of fuel systems are commonly used in modern engines, including a common rail (CR) fuel system and a mechanical unit injector (MUI) fuel system.
A CR fuel system includes a centralized high-pressure pump that feeds pressurized fuel to an accumulator (a.k.a., rail), and a plurality of electronically controlled fuel valves that are supplied with fuel by the accumulator. When a fuel valve inside each injector opens, pressurized fuel from the accumulator flows through an injector nozzle and sprays into an associated combustion chamber.
In contrast to a CR system, a MUI system does not include a centralized high-pressure pump. Instead, the MUI system relies on a cam-driven unit pump for each injector. As a cam rotates to push a lobe against a plunger of the unit pump, high-pressure fuel is forced from the unit pump through an injector nozzle and into an associated combustion chamber.
Competition and government regulations force engine manufacturers to continually improve engine performance, with respect to power, fuel efficiency, and emissions. One way to improve engine performance is to increase fuel injection pressure while also decreasing fuel injection duration. Conventional CR and MUI fuel systems struggle to provide the required higher-pressures within the shorter injection durations.
One attempt to provide a higher performing fuel system is disclosed in U.S. Pat. No. 7,077,101 of Poola et al. that issued on Jul. 18, 2006 (“the '101 patent”). In particular, the '101 patent discloses a hybrid fuel injection system having CR components (i.e., a high-pressure pump that feeds an accumulator or rail) and MUI components (i.e., unit-pump injectors that communicate with the rail). With this arrangement, fuel from the unit pump provides for the main injection of the fuel injector, while fuel from the accumulator provides fuel for one or more auxiliary fuel injections.
Although the hybrid system of the '101 patent may exhibit benefits of a combined CR and MUI system, it may still be less than optimal. In particular, the system may be complex and expensive. In addition, the hybrid system may lack design flexibility and have limited retrofitting capabilities with respect to existing engines.
The fuel system of the present disclosure solves one or more of the problems set forth above.